The surface fibrillar protein Streptococcus mutans designated AgI/II and implicated as a potential protective antigen in immunization against dental caries has been shown to function as an adhesin that enables S. mutans to adhere to tooth surfaces, and to be a target for adherence- inhibiting secretory immunoglobulin A (S-IgA) antibodies. Previous studies have demonstrated the effectiveness of peroral or intranasal immunization with AgI/II chemically coupled to the B subunit of cholera toxin (CTB) in inducing S-IgA antibodies to AgI/II in saliva and other secretions, as well as circulating IgG and IgA antibodies, and in eliciting protective immunity against oral challenge with live S. mutans. To develop this approach to vaccination against dental caries further, the following Specific Aims are proposed. (1) To determine which parts of AgI/II are involved in the adherence of S. mutans to teeth and are recognized by experimental animal and human antibodies, with the object of selecting segments of the molecule most likely to be useful for generating protective immunity. It is thought that protein segments of 10-20kDa will fulfil these criteria. (2) To construct, express, and evaluate genetically engineered combinations of the above-identified regions of AgI/II with CTB, by fusing AgI/II segments to the A2 subunit of cholera toxin and co-expressing these fusion proteins with CTB to generate AgI/II- CTA2/CTB chimeric proteins in recombinant bacteria. (3) To evaluate mucosal (especially salivary) antibody responses (especially S-IgA) to AgI/II-CTA2/CTB chimeric proteins delivered by peroral and intranasal routes, and to evaluate protective immunity to oral infection with S. mutans and the consequent development of dental caries in rats mucosally immunized with AgI/II-CTA2/CTB constructs. The ability of antibodies induced against AgI/II-CTA2/CTB constructs to react with whole AgI/II and with AgI/II-bearing S. mutans will also be determined in functionally relevant assays. (4) To investigate the persistence and recall of salivary S-IgA antibodies induced by mucosal immunization with AgI/II- CTA2/CTB constructs, and the regulatory helper and memory T lymphocytes and the cytokines that they produce, involved in establishing long-term or recallable immunity. These studies are designed to provide the experimental basis for the development of a caries vaccine that can subsequently be evaluated in human trials. The knowledge gained will be applicable in the broader context of developing mucosal vaccines intended to generate protective immunity against not only oral pathogens, but also many others that infect or invade elsewhere through mucosal surfaces.